Certain known and unknown injurious insults to the lung result in a common tissue response of fibrosis. Since fibrosis is the manifestation of fibroblast proliferation and production of extracellular matrix material (ECM), we will examine the control of lung fibroblast proliferation and ECM synthesis and deposition in vitro in an attempt to understand how these processes might be regulated in vivo. Our Aim 1 is to define any differences in the proliferative and ECM synthetic capabilities of normal and fibrotic rat lung fibroblasts. We will begin with rat lung fibroblasts since the animals are rather inexpensive, a bleomycin model for pulmonary fibrosis has been well delineated. In addition, the animal model will allow sampling of lung fibroblasts at different stages of disease. We are especially interested in the early inflammatory state (7 days after bleomycin instillation) and the late fibrotic stage (28 days after bleomycin). Classical conditions have major drawbacks in that they promote fibroblast proliferation and stimulate ECM deposition similar to wound granulation tissue. Thus, these culture conditions may obfuscate any differences among the two types of lung fibroblasts. To circumvent this problem we will determine whether collagen gel matrices which down regulate normal fibroblast proliferation and ECM synthesis will also down regulate fibroblasts from fibrotic lung. Since normal fibroblasts enmershed in collagen gels are quiescent, this may be a superior system for testing the stimulatory potential of agents that might induce fibroblast proliferation and ECM production in vivo. After the baseline differences between normal and fibrotic fibroblasts have been defined, we will determine how various constituents observed in fibrotic lung disease effect both normal and fibrotic lung fibroblasts. Thus, mediators and pulmonary macrophages isolated from bronchoalveolar lavage fluid (BALF) (Aim 2), mast cells and mast cell constituents (Aim 3), and effete neutrophils (Aim 4) will be evaluated for their ability to stimulate fibroblasts. Initial experiments on induction and modulation of normal and fibrotic lung fibroblasts (Aims 2-4) will be accomplished under classic tissue culture conditions. However, if collagen gel systems are shown to down regulate fibroblasts, the modulatory influences of the agents listed in Aims 2-4 will be examined on fibroblasts cultured in or on collagen. We believe that results from these studies will greatly increase our knowledge of the pathogenesis and pathophysiology of ILD and thereby refine our clinical approach to this poorly understood disease.